Conventional articles of footwear have included two primary elements, namely an upper member and a sole structure. The upper member provides a covering for the foot that receives and positions the foot with respect to the sole structure. In addition, the upper member may have a configuration that protects the foot and provides ventilation, thereby cooling the foot and removing perspiration. The sole structure generally is secured to a lower portion of the upper member and generally is positioned between the foot and the contact surface (the terms “contact surface” or “surface,” as used herein, include any foot or footwear contact surface, including but not limited to: grass, dirt, snow, ice, tile, flooring, carpeting, synthetic grass, asphalt, concrete, clay, court surfaces, and the like). In addition to attenuating ground reaction forces, the sole structure may provide traction and help control foot motion, such as pronation. Accordingly, the upper member and the sole structure operate cooperatively to provide a comfortable structure that is suited for a variety of ambulatory activities, such as walking and running.
The sole member of athletic footwear, in at least some instances, will exhibit a layered configuration that includes a comfort-enhancing insole, a resilient midsole (e.g., formed, at least in part, from a polymer foam material), and a ground-contacting outsole that provides both abrasion-resistance and traction. The midsole, in at least some instances, will be the primary sole structure element that attenuates ground reaction forces and controls foot motion. Suitable polymer foam materials for at least portions of the midsole include ethylvinylacetate (“EVA”) or polyurethane (“PU”) that compress resiliently under an applied load to attenuate ground reaction forces. Conventional polymer foam materials are resiliently compressible, in part, due to the inclusion of a plurality of open or closed cells that define an inner volume substantially displaced by gas. The upper member and sole structure in conventional footwear products may be joined to one another in various different ways, such as using cements or adhesives, stitching or sewing, mechanical connectors, fusing techniques, or the like.